The effects of minute vortex generator jet in a turbulent boundary layer with adverse pressure gradient

Experimental and numerical analysis of active and passive flow control is an important topic of practical value in the study of turbulent flows. This paper numerically analyzed the effects of an air microjet on an adverse pressure gradient turbulent boundary layer over a flat plane. Experimental data were employed to verify the numerical modeling. Vortex formation and development were then studied by changing the microjet to inflow velocity ratio (VR) and microjet angles. According to the results, the best values of the angles [Formula: see text] and [Formula: see text] for various velocities were found to be 30° and from 60° to 90°, respectively. Moreover, at VRs = 1, 2, and 4, the [Formula: see text] values (the distance at which the complete vortex persisted in the flow) were 0.058, 0.078, and 0.18, respectively. Compared to VR = 1, the vortex strength for VRs = 2 and 4 grew by 3.5 and 6.8 times, respectively. When the microjet was added to the flow, the highest variation in the Reynolds stress along the x-direction from VR = 1–4 was 10%. The corresponding values along the y and z- directions were 15% and 2.7 times, respectively.

Combined Flow Control of Positively Bowed Blade and Vortex Generator Jet on a Compressor Cascade

A combined flow control method based on positively bowed blade and endwall vortex generator jet (VGJ) was performed to a compressor cascade under three kinds of inlet conditions. The results show that the endwall VGJ can further decrease the total losses in positively bowed cascades. At 0° incidence with zero inlet boundary layer, the separation type in the positively bowed blade is open, with the VGJ, the loss reduction is 2.7 %. As the inlet boundary layer thickens at 0° incidence, the separation region increases with the separation type keeping unchanged, the loss reduction increasing to 11.73 %. As the incidence rises to +7° with zero inlet boundary layer, the separation type converts into closed and the flow separation is the severest in the three cases, with the VGJ, however, the loss reduction is just 7.4 %, which means that the control effect of endwall VGJ not only depends on the size of separation region but also relies on the type of separation mode. If the separation type is open, as the size of separation region expands, the control effectiveness of endwall VGJ increases; if the separation type converts into closed with the further aggravation of flow field, that control effect will decrease.

Effect of End-Wall Vortex Generator Jet Parameters on Flow Control in High Subsonic Compressor Cascade

In order to explore the control mechanism of vortex generator jet, which is located in the passage (PVGJ), on the separation flow, the influence of the pitch angle, skew angle, locations and jet-to-inflow ratio are studied using numerical methods in a high subsonic compressor cascade. The changing of the flow pattern is also analyzed in detail. The results show that the control effect of the end-wall vortex generator jet located in the passage is better than the leading edge one and the aerodynamic performance is effectively improved. The maximum total pressure loss coefficient decreases by 12% and the static pressure coefficient increases by 5.2% while the jet-to-inflow ratio is only 0.3%. The control effect is sensitive to the change of jet parameters. When 0 deg < β < 80 deg, 20 deg < α < 50 deg,, x < 0.5B, y < 0.15t, the vortex generation jet could acquire an ideal control effect. As the jet mass increases, the total pressure loss coefficient gradually reduces. The VGJ prevent separation mainly by bringing high momentum fluid into the near wall region and by promoting momentum transport through turbulent mixing in previous studies. Both the LVGJ and PVGJ mainly take advantage of jet vortex to prevent the cross flow from interacting with the suction side boundary layer.

Effects of Vortex Generator Jet on Flow Separations in Bowed Compressor Cascades

A combined flow control was performed by using a vortex generator jet (VGJ) in bowed compressor cascades. Loss calculations were done over a wide range of parameters including jet mass flow, jet direction and jet location, to determine their effectiveness in controlling flow separation. The topology theory is introduced in this paper to analyze the changes of separation structures in bowed cascades caused by VGJ. The results in this paper indicate that not all kinds of VGJs made up of jet parameters in any arrangement can improve the flow conditions of bowed cascades, but that there are optimal combinations of jet parameters attaining the largest total pressure loss reduction of up to 2.7% and 9.1% for positively and negatively bowed blades, respectively. The VGJ comprised of optimal jet parameters make the flow separation on the suction side of the positively bowed blade basically disappear. The VGJ in the optimal case renders flow separation on the suction side of the negatively bowed blade be relieved so that a separation line on it disappears accordingly. In addition, the mechanisms of VGJs in cases which increase the loss in bowed cascades were chosen to be analyzed in detail. The consequences show that VGJ, in that case, causes that two passage vortices are produced in the positively bowed blade, so the flow field is deteriorated. For the negatively bowed blade, the VGJ leads to the result that the flow separation on the suction side is severer and the separation nodal point corresponding to the corner vortex is transformed from a degenerately nodal point to a spiral point which means that the loss caused by the corner vortex increases.